"Mother's boy" is a term that some people use to describe a boy or man who is very close to his mother and relies on her a lot. It's like when you have a favorite toy that you always like to play with, but instead of a toy, it's your mom.
Some people think that being a mother's boy is not so good because it can mean that the boy or man doesn't learn to be independent and make decisions on his own. It's like if you always ask your mom to help you tie your shoes, you might never learn how to do it by yourself.
But it's also important to remember that having a close relationship with your mom can be a good thing. She can be a source of comfort and support, and she can teach you important things like how to be kind and loving towards others. Just like how your mom helps you with your homework or gives you a hug when you're feeling sad, some boys and men like to stay close to their moms because they feel comfortable and loved around them.